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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Y. Nir 3 Internet-Draft Check Point 4 Obsoletes: 4307 (if approved) T. Kivinen 5 Updates: 7296 (if approved) INSIDE Secure 6 Intended status: Standards Track P. Wouters 7 Expires: October 09, 2016 Red Hat 8 D. Migault 9 Ericsson 10 April 07, 2016 12 Algorithm Implementation Requirements and Usage Guidance for IKEv2 13 draft-ietf-ipsecme-rfc4307bis-07 15 Abstract 17 The IPsec series of protocols makes use of various cryptographic 18 algorithms in order to provide security services. The Internet Key 19 Exchange (IKE) protocol is used to negotiate the IPsec Security 20 Association (IPsec SA) parameters, such as which algorithms should be 21 used. To ensure interoperability between different implementations, 22 it is necessary to specify a set of algorithm implementation 23 requirements and usage guidance to ensure that there is at least one 24 algorithm that all implementations support. This document defines 25 the current algorithm implementation requirements and usage guidance 26 for IKEv2. This document does not update the algorithms used for 27 packet encryption using IPsec Encapsulated Security Payload (ESP). 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on October 09, 2016. 46 Copyright Notice 47 Copyright (c) 2016 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 63 1.1. Updating Algorithm Implementation Requirements and Usage 64 Guidance . . . . . . . . . . . . . . . . . . . . . . . . 3 65 1.2. Updating Algorithm Requirement Levels . . . . . . . . . . 3 66 1.3. Document Audience . . . . . . . . . . . . . . . . . . . . 4 67 2. Conventions Used in This Document . . . . . . . . . . . . . . 4 68 3. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 5 69 3.1. Type 1 - IKEv2 Encryption Algorithm Transforms . . . . . 5 70 3.2. Type 2 - IKEv2 Pseudo-random Function Transforms . . . . 7 71 3.3. Type 3 - IKEv2 Integrity Algorithm Transforms . . . . . . 8 72 3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms . . . . . 9 73 4. IKEv2 Authentication . . . . . . . . . . . . . . . . . . . . 10 74 4.1. IKEv2 Authentication Method . . . . . . . . . . . . . . . 10 75 4.1.1. Recommendations for RSA key length . . . . . . . . . 11 76 4.2. Digital Signature Recommendations . . . . . . . . . . . . 11 77 5. Algorithms for Internet of Things . . . . . . . . . . . . . . 12 78 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 79 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 80 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 81 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 82 9.1. Normative References . . . . . . . . . . . . . . . . . . 14 83 9.2. Informative References . . . . . . . . . . . . . . . . . 14 85 1. Introduction 86 The Internet Key Exchange (IKE) protocol [RFC7296] is used to 87 negotiate the parameters of the IPsec SA, such as the encryption and 88 authentication algorithms and the keys for the protected 89 communications between the two endpoints. The IKE protocol itself is 90 also protected by cryptographic algorithms which are negotiated 91 between the two endpoints using IKE. Different implementations of 92 IKE may negotiate different algorithms based on their individual 93 local policy. To ensure interoperability, a set of "mandatory-to- 94 implement" IKE cryptographic algorithms is defined. 96 This document describes the parameters of the IKE protocol and 97 updates the IKEv2 specification because it changes the mandatory to 98 implement authentication algorithms of the section 4 of the RFC7296 99 by saying RSA key lengths of less than 2048 are SHOULD NOT. It does 100 not describe the cryptographic parameters of the AH or ESP protocols. 102 1.1. Updating Algorithm Implementation Requirements and Usage Guidance 104 The field of cryptography evolves continuously. New stronger 105 algorithms appear and existing algorithms are found to be less secure 106 then originally thought. Therefore, algorithm implementation 107 requirements and usage guidance need to be updated from time to time 108 to reflect the new reality. The choices for algorithms must be 109 conservative to minimize the risk of algorithm compromise. 110 Algorithms need to be suitable for a wide variety of CPU 111 architectures and device deployments ranging from high end bulk 112 encryption devices to small low-power IoT devices. 114 The algorithm implementation requirements and usage guidance may need 115 to change over time to adapt to the changing world. For this reason, 116 the selection of mandatory-to-implement algorithms was removed from 117 the main IKEv2 specification and placed in a separate document. 119 1.2. Updating Algorithm Requirement Levels 121 The mandatory-to-implement algorithm of tomorrow should already be 122 available in most implementations of IKE by the time it is made 123 mandatory. This document attempts to identify and introduce those 124 algorithms for future mandatory-to-implement status. There is no 125 guarantee that the algorithms in use today may become mandatory in 126 the future. Published algorithms are continuously subjected to 127 cryptographic attack and may become too weak or could become 128 completely broken before this document is updated. 130 This document only provides recommendations for the mandatory-to- 131 implement algorithms or algorithms too weak that are recommended not 132 to be implemented. As a result, any algorithm listed at the IKEv2 133 IANA registry not mentioned in this document MAY be implemented. For 134 clarification and consistency with [RFC4307] an algorithm will be set 135 to MAY only when it has been downgraded. 137 Although this document updates the algorithms to keep the IKEv2 138 communication secure over time, it also aims at providing 139 recommendations so that IKEv2 implementations remain interoperable. 140 IKEv2 interoperability is addressed by an incremental introduction or 141 deprecation of algorithms. In addition, this document also considers 142 the new use cases for IKEv2 deployment, such as Internet of Things 143 (IoT). 145 It is expected that deprecation of an algorithm is performed 146 gradually. This provides time for various implementations to update 147 their implemented algorithms while remaining interoperable. Unless 148 there are strong security reasons, an algorithm is expected to be 149 downgraded from MUST to MUST- or SHOULD, instead of MUST NOT. 150 Similarly, an algorithm that has not been mentioned as mandatory-to- 151 implement is expected to be introduced with a SHOULD instead of a 152 MUST. 154 The current trend toward Internet of Things and its adoption of IKEv2 155 requires this specific use case to be taken into account as well. 156 IoT devices are resource constrained devices and their choice of 157 algorithms are motivated by minimizing the footprint of the code, the 158 computation effort and the size of the messages to send. This 159 document indicates "[IoT]" when a specified algorithm is specifically 160 listed for IoT devices. 162 1.3. Document Audience 164 The recommendations of this document mostly target IKEv2 implementers 165 as implementations need to meet both high security expectations as 166 well as high interoperability between various vendors and with 167 different versions. Interoperability requires a smooth move to more 168 secure cipher suites. This may differ from a user point of view that 169 may deploy and configure IKEv2 with only the safest cipher suite. On 170 the other hand, comments and recommendations from this document are 171 also expected to be useful for such users. 173 IKEv1 is out of scope of this document. IKEv1 is deprecated and the 174 recommendations of this document must not be considered for IKEv1, as 175 most IKEv1 implementations have been "frozen" and will not be able to 176 update the list of mandatory-to-implement algorithms. 178 2. Conventions Used in This Document 179 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 180 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 181 document are to be interpreted as described in [RFC2119]. 183 We define some additional terms here: 185 SHOULD+ This term means the same as SHOULD. However, it is likely 186 that an algorithm marked as SHOULD+ will be promoted at some 187 future time to be a MUST. 188 SHOULD- This term means the same as SHOULD. However, an algorithm 189 marked as SHOULD- may be deprecated to a MAY in a future 190 version of this document. 191 MUST- This term means the same as MUST. However, we expect at some 192 point that this algorithm will no longer be a MUST in a 193 future document. Although its status will be determined at a 194 later time, it is reasonable to expect that if a future 195 revision of a document alters the status of a MUST- 196 algorithm, it will remain at least a SHOULD or a SHOULD- 197 level. 198 IoT stands for Internet of Things. 200 Table 1 202 3. Algorithm Selection 204 3.1. Type 1 - IKEv2 Encryption Algorithm Transforms 206 The algorithms in the below table are negotiated in the SA payload 207 and used for the Encrypted Payload. References to the specification 208 defining these algorithms and the ones in the following subsections 209 are in the IANA registry [IKEV2-IANA]. Some of these algorithms are 210 Authenticated Encryption with Associated Data (AEAD - [RFC5282]). 211 Algorithms that are not AEAD MUST be used in conjunction with an 212 integrity algorithms in Section 3.3. 214 +-----------------------------+----------+-------+----------+ 215 | Name | Status | AEAD? | Comment | 216 +-----------------------------+----------+-------+----------+ 217 | ENCR_AES_CBC | MUST- | No | [1] | 218 | ENCR_CHACHA20_POLY1305 | SHOULD | Yes | | 219 | AES-GCM with a 16 octet ICV | SHOULD | Yes | [1] | 220 | ENCR_AES_CCM_8 | SHOULD | Yes | [1][IoT] | 221 | ENCR_3DES | MAY | No | | 222 | ENCR_DES | MUST NOT | No | | 223 +-----------------------------+----------+-------+----------+ 225 [1] - This requirement level is for 128-bit keys. 256-bit keys are at 226 SHOULD. 192-bit keys can safely be ignored. [IoT] - This requirement 227 is for interoperability with IoT. 229 Table 2 231 ENCR_AES_CBC is raised from SHOULD+ in [RFC4307] to MUST. It is the 232 only shared mandatory-to-implement algorithm with RFC4307 and as a 233 result it is necessary for interoperability with IKEv2 implementation 234 compatible with RFC4307. 236 ENCR_CHACHA20_POLY1305 was not ready to be considered at the time of 237 RFC4307. It has been recommended by the CRFG and others as an 238 alternative to AES-CBC and AES-GCM. It is also being standardized 239 for IPsec for the same reasons. At the time of writing, there were 240 not enough IKEv2 implementations supporting ENCR_CHACHA20_POLY1305 to 241 be able to introduce it at the SHOULD+ level. 243 AES-GCM with a 16 octet ICV was not considered in RFC4307. At the 244 time RFC4307 was written, AES-GCM was not defined in an IETF 245 document. AES-GCM was defined for ESP in [RFC4106] and later for 246 IKEv2 in [RFC5282]. The main motivation for adopting AES-GCM for ESP 247 is encryption performance and key longevity compared to AES-CBC. 248 This resulted in AES-GCM being widely implemented for ESP. As the 249 computation load of IKEv2 is relatively small compared to ESP, many 250 IKEv2 implementations have not implemented AES-GCM. For this reason, 251 AES-GCM is not promoted to a greater status than SHOULD. The reason 252 for promotion from MAY to SHOULD is to promote the slightly more 253 secure AEAD method over the traditional encrypt+auth method. Its 254 status is expected to be raised once widely implemented. As the 255 advantage of the shorter (and weaker) ICVs is minimal, the 8 and 12 256 octet ICV's remain at the MAY level. 258 ENCR_AES_CCM_8 was not considered in RFC4307. This document 259 considers it as SHOULD be implemented in order to be able to interact 260 with Internet of Things devices. As this case is not a general use 261 case for non-IoT VPNs, its status is expected to remain as SHOULD. 262 The 8 octet size of the ICV is expected to be sufficient for most use 263 cases of IKEv2, as far less packets are exchanged on those cases, and 264 IoT devices want to make packets as small as possible. When 265 implemented, ENCR_AES_CCM_8 MUST be implemented for key length 128 266 and MAY be implemented for key length 256. 268 ENCR_3DES has been downgraded from RFC4307 MUST- to SHOULD NOT. All 269 IKEv2 implementation already implement ENCR_AES_CBC, so there is no 270 need to keep support for the much slower ENCR_3DES. In addition, 271 ENCR_CHACHA20_POLY1305 provides a more modern alternative to AES. 273 ENCR_DES can be brute-forced using of-the-shelves hardware. It 274 provides no meaningful security whatsoever and therefor MUST NOT be 275 implemented. 277 3.2. Type 2 - IKEv2 Pseudo-random Function Transforms 279 Transform Type 2 algorithms are pseudo-random functions used to 280 generate pseudo-random values when needed. 282 If an algorithm is selected as the integrity algorithm, it SHOULD 283 also be used as the PRF. When using an AEAD cipher, a choice of PRF 284 needs to be made. The table below lists the recommended algorithms. 286 +-------------------+----------+---------+ 287 | Name | Status | Comment | 288 +-------------------+----------+---------+ 289 | PRF_HMAC_SHA2_256 | MUST | | 290 | PRF_HMAC_SHA2_512 | SHOULD+ | | 291 | PRF_HMAC_SHA1 | MUST- | | 292 | PRF_AES128_XCBC | SHOULD | [IoT] | 293 | PRF_HMAC_MD5 | MUST NOT | | 294 +-------------------+----------+---------+ 296 [IoT] - This requirement is for interoperability with IoT 298 Table 3 300 PRF_HMAC_SHA2_256 was not mentioned in RFC4307, as no SHA2 based 301 transforms were mentioned. PRF_HMAC_SHA2_256 MUST be implemented in 302 order to replace SHA1 and PRF_HMAC_SHA1. 304 PRF_HMAC_SHA2_512 SHOULD be implemented as a future replacement for 305 PRF_HMAC_SHA2_256 or when stronger security is required. 306 PRF_HMAC_SHA2_512 is preferred over PRF_HMAC_SHA2_384, as the 307 additional overhead of PRF_HMAC_SHA2_512 is negligible. 309 PRF_HMAC_SHA1 has been downgraded from MUST in RFC4307 to MUST- as 310 their is an industry-wide trend to deprecate its usage. 312 PRF_AES128_XCBC is only recommended in the scope of IoT, as Internet 313 of Things deployments tend to prefer AES based pseudo-random 314 functions in order to avoid implementing SHA2. For the non-IoT VPN 315 deployment it has been downgraded from SHOULD in RFC4307 to MAY as it 316 has not seen wide adoption. 318 PRF_HMAC_MD5 has been downgraded from MAY in RFC4307 to MUST NOT. 319 There is an industry-wide trend to deprecate its usage as MD5 support 320 is being removed from cryptographic libraries in general because its 321 non-HMAC use is known to be subject to collision attacks, for example 322 as mentioned in [TRANSCRIPTION]. 324 3.3. Type 3 - IKEv2 Integrity Algorithm Transforms 326 The algorithms in the below table are negotiated in the SA payload 327 and used for the Encrypted Payload. References to the specification 328 defining these algorithms are in the IANA registry. When an AEAD 329 algorithm (see Section 3.1) is proposed, this algorithm transform 330 type is not in use. 332 +------------------------+----------+---------+ 333 | Name | Status | Comment | 334 +------------------------+----------+---------+ 335 | AUTH_HMAC_SHA2_256_128 | MUST | | 336 | AUTH_HMAC_SHA2_512_256 | SHOULD | | 337 | AUTH_HMAC_SHA1_96 | MUST- | | 338 | AUTH_AES_XCBC_96 | SHOULD | [IoT] | 339 | AUTH_HMAC_MD5_96 | MUST NOT | | 340 | AUTH_DES_MAC | MUST NOT | | 341 | AUTH_KPDK_MD5 | MUST NOT | | 342 +------------------------+----------+---------+ 344 [IoT] - This requirement is for interoperability with IoT 346 Table 4 348 AUTH_HMAC_SHA2_256_128 was not mentioned in RFC4307, as no SHA2 based 349 transforms were mentioned. AUTH_HMAC_SHA2_256_128 MUST be 350 implemented in order to replace AUTH_HMAC_SHA1_96. 352 AUTH_HMAC_SHA2_512_256 SHOULD be implemented as a future replacement 353 of AUTH_HMAC_SHA2_256_128 or when stronger security is required. 354 This value has been preferred over AUTH_HMAC_SHA2_384, as the 355 additional overhead of AUTH_HMAC_SHA2_512 is negligible. 357 AUTH_HMAC_SHA1_96 has been downgraded from MUST in RFC4307 to MUST- 358 as there is an industry-wide trend to deprecate its usage. 360 AUTH_AES-XCBC is only recommended in the scope of IoT, as Internet of 361 Things deployments tend to prefer AES based pseudo-random functions 362 in order to avoid implementing SHA2. For the non-IoT VPN deployment, 363 it has been downgraded from SHOULD in RFC4307 to MAY as it has not 364 been widely adopted. 366 AUTH_HMAC_MD5_96, AUTH_DES_MAC and AUTH_KPDK_MD5 were not mentioned 367 in RFC4307 so its default status was MAY. It has been downgraded to 368 MUST NOT. There is an industry-wide trend to deprecate its usage. 370 MD5 support is being removed from cryptographic libraries in general 371 because its non-HMAC use is known to be subject to collision attacks, 372 for example as mentioned in [TRANSCRIPTION]. 374 3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms 376 There are several Modular Exponential (MODP) groups and several 377 Elliptic Curve groups (ECC) that are defined for use in IKEv2. These 378 groups are defined in both the [IKEv2] base document and in 379 extensions documents and are identified by group number. Note that 380 it is critical to enforce a secure Diffie-Hellman exchange as this 381 exchange provides keys for the session. If an attacker can retrieve 382 the private numbers (a, or b) and the public values (g**a, and g**b), 383 then the attacker can compute the secret and the keys used and 384 decrypt the exchange and IPsec SA created inside the IKEv2 SA. Such 385 an attack can be performed off-line on a previously recorded 386 communication, years after the communication happened. This differs 387 from attacks that need to be executed during the authentication which 388 must be performed online and in near real-time. 390 +------------+----------------------------------------+-------------+ 391 | Number | Description | Status | 392 +------------+----------------------------------------+-------------+ 393 | 14 | 2048-bit MODP Group | MUST | 394 | 19 | 256-bit random ECP group | SHOULD | 395 | 5 | 1536-bit MODP Group | SHOULD NOT | 396 | 2 | 1024-bit MODP Group | SHOULD NOT | 397 | 1 | 768-bit MODP Group | MUST NOT | 398 | 22 | 1024-bit MODP Group with 160-bit Prime | SHOULD NOT | 399 | | Order Subgroup | | 400 | 23 | 2048-bit MODP Group with 224-bit Prime | SHOULD NOT | 401 | | Order Subgroup | | 402 | 24 | 2048-bit MODP Group with 256-bit Prime | SHOULD NOT | 403 | | Order Subgroup | | 404 +------------+----------------------------------------+-------------+ 406 Table 5 408 Group 14 or 2048-bit MODP Group is raised from SHOULD+ in RFC4307 as 409 a replacement for 1024-bit MODP Group. Group 14 is widely 410 implemented and considered secure. 412 Group 19 or 256-bit random ECP group was not specified in RFC4307, as 413 this group were not specified at that time. Group 19 is widely 414 implemented and considered secure. 416 Group 5 or 1536-bit MODP Group has been downgraded from MAY in 417 RFC4307 to SHOULD NOT. It was specified earlier, but is now 418 considered to be vulnerable to be broken within the next few years by 419 a nation state level attack, so its security margin is considered too 420 narrow. 422 Group 2 or 1024-bit MODP Group has been downgraded from MUST- in 423 RFC4307 to SHOULD NOT. It is known to be weak against sufficiently 424 funded attackers using commercially available mass-computing 425 resources, so its security margin is considered too narrow. It is 426 expected in the near future to be downgraded to MUST NOT. 428 Group 1 or 768-bit MODP Group was not mentioned in RFC4307 and so its 429 status was MAY. It can be broken within hours using cheap of-the- 430 shelves hardware. It provides no security whatsoever. 432 Group 22, 23 and 24 or 1024-bit MODP Group with 160-bit, and 2048-bit 433 MODP Group with 224-bit and 256-bit Prime Order Subgroup have small 434 subgroups, which means that checks specified in the "Additional 435 Diffie-Hellman Test for the IKEv2" [RFC6989] section 2.2 first bullet 436 point MUST be done when these groups are used. These groups are also 437 not safe-primes. The seeds for these groups have not been publicly 438 released, resulting in reduced trust in these groups. These groups 439 were proposed as alternatives for group 2 and 14 but never saw wide 440 deployment. It is expected in the near future to be further 441 downgraded to MUST NOT. 443 4. IKEv2 Authentication 445 IKEv2 authentication may involve a signatures verification. 446 Signatures may be used to validate a certificate or to check the 447 signature of the AUTH value. Cryptographic recommendations regarding 448 certificate validation are out of scope of this document. What is 449 mandatory to implement is provided by the PKIX Community. This 450 document is mostly concerned on signature verification and generation 451 for the authentication. 453 4.1. IKEv2 Authentication Method 455 +--------+---------------------------------------+------------+ 456 | Number | Description | Status | 457 +--------+---------------------------------------+------------+ 458 | 1 | RSA Digital Signature | MUST | 459 | 2 | Shared Key Message Integrity Code | MUST | 460 | 3 | DSS Digital Signature | SHOULD NOT | 461 | 9 | ECDSA with SHA-256 on the P-256 curve | SHOULD | 462 | 10 | ECDSA with SHA-384 on the P-384 curve | SHOULD | 463 | 11 | ECDSA with SHA-512 on the P-521 curve | SHOULD | 464 | 14 | Digital Signature | SHOULD | 465 +--------+---------------------------------------+------------+ 466 Table 6 468 RSA Digital Signature is widely deployed and therefore kept for 469 interoperability. It is expected to be downgraded in the future as 470 its signatures are based on the older RSASSA-PKCS1-v1.5 which is no 471 longer recommended. RSA authentication, as well as other specific 472 Authentication Methods, are expected to be replaced with the generic 473 Digital Signature method of [RFC7427]. RSA Digital Signature is not 474 recommended for keys smaller then 2048, but since these signatures 475 only have value in real-time, and need no future protection, smaller 476 keys was kept at SHOULD NOT instead of MUST NOT. 478 Shared Key Message Integrity Code is widely deployed and mandatory to 479 implement in the IKEv2 in the RFC7296. 481 ECDSA based Authentication Methods are also expected to be downgraded 482 as it does not provide hash function agility. Instead, ECDSA (like 483 RSA) is expected to be performed using the generic Digital Signature 484 method. 486 DSS Digital Signature is bound to SHA-1 and has the same level of 487 security as 1024-bit RSA. It is expected to be downgraded to MUST 488 NOT in the future. 490 Digital Signature [RFC7427] is expected to be promoted as it provides 491 hash function, signature format and algorithm agility. 493 4.1.1. Recommendations for RSA key length 495 +-------------------------------------------+------------+ 496 | Description | Status | 497 +-------------------------------------------+------------+ 498 | RSA with key length 2048 | MUST | 499 | RSA with key length 3072 and 4096 | SHOULD | 500 | RSA with key length between 2049 and 4095 | MAY | 501 | RSA with key length smaller than 2048 | SHOULD NOT | 502 +-------------------------------------------+------------+ 504 Table 7 506 The IKEv2 RFC7296 mandates support for the RSA keys of size 1024 or 507 2048 bits, but here we make key sizes less than 2048 SHOULD NOT as 508 there is industry-wide trend to deprecate key lengths less than 2048 509 bits. 511 4.2. Digital Signature Recommendations 513 Recommendations for when a hash function is involved in a signature: 515 +--------+-------------+------------+---------+ 516 | Number | Description | Status | Comment | 517 +--------+-------------+------------+---------+ 518 | 1 | SHA1 | SHOULD NOT | | 519 | 2 | SHA2-256 | MUST | | 520 | 3 | SHA2-384 | MAY | | 521 | 4 | SHA2-512 | SHOULD | | 522 +--------+-------------+------------+---------+ 524 Table 8 526 With the use of Digital Signature, RSASSA-PKCS1-v1.5 MAY be 527 implemented. RSASSA-PSS MUST be implemented. 529 Recommendation of Authentication Method described in [RFC7427] 530 notation: 532 +------------------------------------+------------+---------+ 533 | Description | Status | Comment | 534 +------------------------------------+------------+---------+ 535 | RSASSA-PSS with SHA-256 | SHOULD | | 536 | ecdsa-with-sha256 | SHOULD | | 537 | sha1WithRSAEncryption | SHOULD NOT | | 538 | dsa-with-sha1 | SHOULD NOT | | 539 | ecdsa-with-sha1 | SHOULD NOT | | 540 | RSASSA-PSS with Empty Parameters | SHOULD NOT | | 541 | RSASSA-PSS with Default Parameters | SHOULD NOT | | 542 +------------------------------------+------------+---------+ 544 Table 9 546 5. Algorithms for Internet of Things 548 Some algorithms in this document are marked for use with the Internet 549 of Things (IoT). There are several reasons why IoT devices prefer a 550 different set of algorithms from regular IKEv2 clients. IoT devices 551 are usually very constrained, meaning the memory size and CPU power 552 is so limited, that these clients only have resources to implement 553 and run one set of algorithms. For example, instead of implementing 554 AES and SHA, these devices typically use AES_XCBC as integrity 555 algorithm so SHA does not need to be implemented. 557 For example, IEEE Std 802.15.4 [IEEE-802-15-4] devices have a 558 mandatory to implement link level security using AES-CCM with 128 bit 559 keys. The IEEE Recommended Practice for Transport of Key Management 560 Protocol (KMP) Datagrams [IEEE-802-15-9] already provide a way to use 561 Minimal IKEv2 [RFC7815] over 802.15.4 to provide link keys for the 562 802.15.4 layer. 564 These devices might want to use AES-CCM as their IKEv2 algorithm, so 565 they can reuse the hardware implementing it. They cannot use the 566 AES-CBC algorithm, as the hardware quite often do not include support 567 for AES decryption needed to support the CBC mode. So despite the 568 AES-CCM algorithm requiring AEAD [RFC5282] support, the benefit of 569 reusing the crypto hardware makes AES-CCM the preferred algorithm. 571 Another important aspect of IoT devices is that their transfer rates 572 are usually quite low (in order of tens of kbits/s), and each bit 573 they transmit has an energy consumption cost associated with it and 574 shortens their battery life. Therefore, shorter packets are 575 preferred. This is the reason for recommending the 8 octet ICV over 576 the 16 octet ICV. 578 Because different IoT devices will have different constraints, this 579 document cannot specify the one mandatory profile for IoT. Instead, 580 this document points out commonly used algorithms with IoT devices. 582 6. Security Considerations 584 The security of cryptographic-based systems depends on both the 585 strength of the cryptographic algorithms chosen and the strength of 586 the keys used with those algorithms. The security also depends on 587 the engineering of the protocol used by the system to ensure that 588 there are no non-cryptographic ways to bypass the security of the 589 overall system. 591 The Diffie-Hellman Group parameter is the most important one to 592 choose conservatively. Any party capturing all IKE and ESP traffic 593 that (even years later) can break the selected DH group in IKE, can 594 gain access to the symmetric keys used to encrypt all the ESP 595 traffic. Therefore, these groups must be chosen very conservatively. 596 However, specifying an extremely large DH group also puts a 597 considerable load on the device, especially when this is a large VPN 598 gateway or an IoT constrained device. 600 This document concerns itself with the selection of cryptographic 601 algorithms for the use of IKEv2, specifically with the selection of 602 "mandatory-to-implement" algorithms. The algorithms identified in 603 this document as "MUST implement" or "SHOULD implement" are not known 604 to be broken at the current time, and cryptographic research so far 605 leads us to believe that they will likely remain secure into the 606 foreseeable future. However, this isn't necessarily forever and it 607 is expected that new revisions of this document will be issued from 608 time to time to reflect the current best practice in this area. 610 7. IANA Considerations 611 This document makes no requests of IANA. 613 8. Acknowledgements 615 The first version of this document was RFC 4307 by Jeffrey I. 616 Schiller of the Massachusetts Institute of Technology (MIT). Much of 617 the original text has been copied verbatim. 619 We would like to thank Paul Hoffman, Yaron Sheffer, John Mattsson and 620 Tommy Pauly for their valuable feedback. 622 9. References 624 9.1. Normative References 626 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 627 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 628 RFC2119, March 1997, 629 . 631 [RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode 632 (GCM) in IPsec Encapsulating Security Payload (ESP)", RFC 633 4106, DOI 10.17487/RFC4106, June 2005, 634 . 636 [RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the 637 Internet Key Exchange Version 2 (IKEv2)", RFC 4307, DOI 638 10.17487/RFC4307, December 2005, 639 . 641 [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. 642 Kivinen, "Internet Key Exchange Protocol Version 2 643 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 644 2014, . 646 [RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption 647 Algorithms with the Encrypted Payload of the Internet Key 648 Exchange version 2 (IKEv2) Protocol", RFC 5282, DOI 649 10.17487/RFC5282, August 2008, 650 . 652 9.2. Informative References 654 [RFC7427] Kivinen, T. and J. Snyder, "Signature Authentication in 655 the Internet Key Exchange Version 2 (IKEv2)", RFC 7427, 656 DOI 10.17487/RFC7427, January 2015, 657 . 659 [RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman 660 Tests for the Internet Key Exchange Protocol Version 2 661 (IKEv2)", RFC 6989, DOI 10.17487/RFC6989, July 2013, 662 . 664 [RFC7815] Kivinen, T., "Minimal Internet Key Exchange Version 2 665 (IKEv2) Initiator Implementation", RFC 7815, DOI 10.17487/ 666 RFC7815, March 2016, 667 . 669 [IKEV2-IANA] 670 , "Internet Key Exchange Version 2 (IKEv2) Parameters", , 671 . 673 [TRANSCRIPTION] 674 Bhargavan, K. and G. Leurent, "Transcript Collision 675 Attacks: Breaking Authentication in TLS, IKE, and SSH", 676 NDSS , feb 2016. 678 [IEEE-802-15-4] 679 , "IEEE Standard for Low-Rate Wireless Personal Area 680 Networks (WPANs)", IEEE Standard 802.15.4, 2015. 682 [IEEE-802-15-9] 683 , "IEEE Recommended Practice for Transport of Key 684 Management Protocol (KMP) Datagrams", IEEE Standard 685 802.15.9, 2016. 687 Authors' Addresses 689 Yoav Nir 690 Check Point Software Technologies Ltd. 691 5 Hasolelim st. 692 Tel Aviv 6789735 693 Israel 695 EMail: ynir.ietf@gmail.com 697 Tero Kivinen 698 INSIDE Secure 699 Eerikinkatu 28 700 HELSINKI FI-00180 701 FI 703 EMail: kivinen@iki.fi 704 Paul Wouters 705 Red Hat 707 EMail: pwouters@redhat.com 709 Daniel Migault 710 Ericsson 711 8400 boulevard Decarie 712 Montreal, QC H4P 2N2 713 Canada 715 Phone: +1 514-452-2160 716 EMail: daniel.migault@ericsson.com